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Hosts of Bipolaris Sorokiniana, the Major Pathogen of Spot Blotch of Wheat in Pakistan

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Hosts of Bipolaris Sorokiniana, the Major Pathogen of Spot Blotch of Wheat in Pakistan Pak . J. Bot., 41(3): 1433-1436, 2009. HOSTS OF BIPOLARIS SOROKINIANA, THE MAJOR PATHOGEN OF SPOT BLOTCH OF WHEAT IN PAKISTAN SHAMIM IFTIKHAR, SHAHZAD ASAD, ANJUM MUNIR, AMIR SULTAN AND IFTIKHAR AHMAD* Crop Diseases Research Program, Institute of Plant and Environmental Protection, National Agricultural Research Centre, Park Road, Islamabad-45500, Pakistan *National Agricultural Research Centre Abstract Bipolaris sorokiniana (Sacc.) Shoemaker (teleomorph Cochliobolus sativus) is the causal agent of common root rot, leaf spot and seedling blight, head blight of wheat and barley and black point of grains. It causes significant yield losses in South Asian countries and considered as a serious foliar disease constraints in warmer growing areas. Numerous plant species other than wheat and barley are identified as the host of B. sorokiniana world wide. Fifteen crops including Arachis hypogea, Avena sativa, Brassica compestris, Cicer arientenum, Glycine max, Halianthus annus,Hordeum vulgare, Lens culinaris,Oryza sativa, Pennisetum amaricanum,Sesamum indicum, Sorghum bicolor, Vigna mungo, Vigna radiata, and Zea mays which are grown in different agro-ecological zones of wheat production were tested against local isolate of B. sorokiniana by In vitro technique. Eleven crops viz., Avena sativa, Hordeum vulgare, Brassica compestris, Glycine max, Lens culinaris, Vigna radiata, Sesamum indicum, Vigna mungo, Sorghum bicolor, Zea mays and Pennisetum amaricanum are found to be the hosts of B. sorokiniana. Introduction Bipolaris sorokiniana (Sacc.) Shoemaker (Sivanesan, 1990) is a seed and soil borne pathogen, causes head blight, seedling blight, foliar blight/ spot blotch, common root rot and black point of wheat, barley and other small cereal grains and grasses (Wiese, 1998). It is considered as one of the most important wheat pathogen in the warmer areas of the world (Dubin & Van Ginkel, 1991). In the Southern province of Sindh, where winter temperatures are warmer, Helminthosporium leaf blight has been reported (Bhatti & Ilyas, 1986; Hafiz, 1986) and the pathogen causes significant yield losses (Aftabuddin et al., 1991). High temperature and high relative humidity favour the outbreak of the disease (Aggarwal et al., 2000). Plant with common root rot produces fewer tillers and fewer kernels per ear. Under favourable conditions, spikelets may be affected, causing grain shriveling, it can initiate epidemics by infecting the primary leaf via the coleoptile during seedling emergence and heavily infected seedlings may fail to emerge (Kumar et al., 2002). Due to this destructive pathogen, the yield loss was estimated at 18-22% in India (Singh et al., 1997) and 23.8% in Nepal (Shrestha et al., 1997). The pathogen causes grain yield losses up to 15, 10 and 20 % through common root rot and seedling blight in Canada, Scotland and Brazil respectively (Murray et al., 1998). The presence of other hosts plays an important role in disease epidemic. The primary inoculum of B. sorokiniana comes from several sources such as weed hosts, soil, crop debris which enhances the disease level. The grass weeds as a collateral host of B. sorokiniana in rice–wheat system is considered as a possible reason for perceived increase in Helminthosporium leaf blight and cause major losses to the crop (Hobbs & Morris, 1996). The perennial nature of some grasses and their presence in wheat growing 1434 SHAMIM IFTIKHAR ET AL., areas is reported to facilitate over wintering and survival of the pathogen. The crop rotation with non-host plants reduces the impact of leaf diseases by separating the new wheat crop from existing inoculum sources. The most common and beneficial rotation has been found by leguminous crops (Chang & Wu, 1998). Thus initial study was under taken to confirm such hosts which are grown in wheat growing areas and where pathogen gets shelter for their survival. This can be helpful ultimately in designing the management strategies in future. Materials and methods Preparation of inoculum: The isolate was collected from zone 5 (Khanewal) which was considered the most aggressive isolate (Iftikhar et al., 2006; Asad, et al., 2007) in previous studies, was used in this study. The pure mother culture of Bipolaris sorokiniana was multiplied on potato dextrose agar medium (PDA). The inoculated PDA plates were incubated at 22oC ± 3oC for 12 days till the full growth of the fungus was observed on the media and then these cultures were used as inoculum. In vitro test: Fifteen crops including Avena sativa (oats), Arachis hypogea (peanut), Brassica campestris (sarsoon), Cicer arientenum (chickpea), Glycine max (soybean), Hordeum vulgare (barley), Halianthus annus (sunflower), Lens culinaris (lentil), Pennisetum amaricanum (millet), Oryza sativa (rice), Sesamum indicum (sesamum), Sorghum bicolor (sorghum), Vigna radiata (mash), Vigna mungo (mung) and Zea mays (maize) were tested for the infection of the pathogen B. sorokiniana by In-vitro method (Iftikhar et al., 2007). Test tubes (29cm x 3cm) were filled with one fourth cotton swab from the bottom. Twenty ml distilled water was added to each test tube to moist the cotton and were covered with aluminum foil. The test tubes were autoclaved and upon cooling were used for inoculation. Seeds of each crop were surface disinfected with 1% Clorox solution for one minute and rinsed twice with sterilized distilled water. Three seeds of each crop were placed in test tube on cotton swab in triplicate along with one disc of 5 mm culture of B. sorokiniana. The inoculum potential was 3.2 x 104 conidia/ disc. After inoculation, the mouth of each test tube was covered with aluminum foil and was incubated at 25oC in growth chamber. After 30 days data was recorded. Symptoms on foliar parts were recorded by noting the presence and absence of lesions on the leaves developed by the infection of the pathogen. The pathogen was re isolated and compared with the mother culture. Results and Discussion The typical spot blotch symptoms were produced on the leaves of 11 crops including Avena sativa (oats), Brassica campestris (sarsoon), Glycine max (soybean), Hordeum vulgare (barley), Lens culinaris (lentil), Pennisetum amaricanum (millet), Sesamum indicum (sesamum), Sorghum bicolor (sorghum), Vigna radiata (mash), Vigna mungo (mung) and Zea mays (maize) under In vitro conditions (Table 1). The pathogen was re- isolated and found alike with mother culture upon microscopy. Out of these hosts Hordeum vulgare, Avena sativa, Cicer arientenum, Sorghum bicolor and Zea maize have already been reported as hosts of B. sorokiniana (Jones & Cliford, 1983, ARS Fungal Database-http://nt.ars-grin.gov/fungaldatabases), however Zillinsky (1983) reported that rye is less susceptible and oats are seldom infected. HOSTS OF BIPOLARIS SOROKINIANA IN PAKISTAN 1435 Table 1. Status of crops as hosts of Bipolaris sorokiniana other than wheat. S. No. Crop (common name) Status 1. Avena sativa (oats) + 2. Arachis hypogea (Peanut) - 3. Brassica compestris (sarsoon) + 4. Cicer arientenum (Chickpea) - 5. Glycine max (Soybean) + 6. Hordeum vulgare (Barley) + 7. Halianthus annus (Sunflower) - 8. Lens culinaris (Lentil) + 9. Pennisetun amaricanum (Millet) + 10. Oryza sativa (Rice) - 11. Sesamum indicum (Sesamum) + 12. Sorghum bicolor (Sorghum) + 13. Vigna radiate (Mash) + 14. Vigna mungo (Mung) + 15. Zea mays (Maize) + The results of our studies revealed that the plants of Oryza sativa, Halianthus annus, Arachis hypogea and Cicer arientenum were non host of Bipolaris sorokiniana, which are in contrast to the results which are reported in USDA ARS Fungal Database- http://nt.ars-grin.gov/fungaldatabases, where Cicer arientenum and Oryza sativa are reported as a host of B. sorokiniana. The results on these crops still need confirmation as these crops along with other weed grass species in the wheat field helps in survival of this pathogen (Jones & Clifford, 1983). This pathogen infects number of both cultivated and wild plants. Eighteen monocotyledonous plants have been identified as its hosts (Balogh et al., 1991). More than 29 species of Graminae and other crops in Northeastern China, 65 species of Graminae in Yellow and hai river region and 17 plant species in Guandong province are reported as the hosts of this pathogen (Chang & Wu, 1997). Keeping in view the wide host ranges of this fungus and on the basis of these preliminary studies further detailed investigations needed to be done which will ultimately help in sorting the spot blotch management. As one of the strategy to manage the disease is to rotate the crops with oat, rye, legumes or flax to reduce source of fungal spores from residue (http://www.ipmcenters.org/cropprofiles/docs/NDbarley.html). References Aftabuddin, A., W.E. Grey, D.E. Mathre and A.L. Scharen. 1991. Resistance in spring wheat to common root rot, spot blotch and black point caused by Cochliobolus sativus. Proc. First Int. Workshop on Common Root Rot of Cereals. Saskatoon, Canada. 11-14 August 1991. pp: 45-47. Aggarwal, P.K., K.K. Talukdar and R.K. Mall. 2000. Potential yields of rice- wheat system in the Indo-Gangetic Plains of India. Consortium paper series 10. Rice-wheat consortium for the Indo-Gangetic Plains, New Delhi, India. pp. 16. Asad, S., S. Iftikhar, A. Munir, I. Ahmad and N. Ayub. 2007. Pathogenic Diversity in Bipolaris sorokiniana isolates collected from different wheat growing areas of Punjab and NWFP of Pakistan. Pak. J. Bot., 39(6): 2225 - 2231. Balogh, S., R. Ratai, I. Aponyi, A. Schweigert and I. Fuzi. 1991. A kalaszosok helmintosporiumos levelszaradasa. (Helminththosporium blights of cereals). KSZE, Agroforum, majusi kulonszam, pp. 30-33. In: Helminthosporium Blight of Wheat: Spot Blotch and Tan Spot. (Eds.): E. Duveiller, H.J. Dubin, J. Reeves and A. McNab. Mexico, D. F., Mexico: CIMMYT, pp. 80-85. 1436 SHAMIM IFTIKHAR ET AL., Bhatti, M.A.R. and M.B. Ilyas. 1986. Wheat diseases in Pakistan. In: Problems and progress of Wheat in South Asia. (Eds.): L.M. Joshi, D.V. Singh and K.D. Srivastava. pp. 20-30. New Dehli, India. Malhotra publishing house. 401 pp. Chang, N. and Y.
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